1. Field of the Invention
The present invention relates to a device for distributive dot printing for a printer. The device according to the present invention can be used for a serial printer of the wire dot type.
2. Description of the Related Arts
In general, an electromagnetic coil is used for actuaitng the head pins or dot wires of a printing head. The electromagnetic coil is energized from a power source.
When a graphic pattern such as a broad solid line pattern is printed, approximately the maximum capacity of the power source is needed for the printing. On the other hand, when a character or numeral pattern is printed, only approximately 20% in average and approximately 33% at maximum of the maximum capacity of the power source is needed for the printing.
Under these conditions, it is not economical to provide a power source having a capacity corresponding to that require for the printing of an entire block pattern. Accordingly, the design capcity of the power source for such a printer is usually approximately 33% of the maximum value required.
If the design capacity of the power source is approximately 33% of the maximum value as described above, the source voltage for the energization of the printing head for carrying out printing of a graphic pattern will sometimes fall below the necessary voltage and the graphic pattern cannot be printed. To counter such a situation, the method of divisional printing has been used for cases where the source voltage is insufficient.
In the divisional printing method, the head pins in the printing head are divided into two or three groups and the groups individually energized. A dot pattern in one row is thus printed divisionally, for example, in two steps or in three steps. For two-step divisional printing, the design capacity of the power source can be made approximately 50% of the maximum value. For three-step divisional printing, the design capacity of the power source can be made approximately 33% of maximum value.
When the above-described divisional printing is applied to the paper on the platen, during the plural steps of divisional printing, the printing device does not feed the paper forward. However, as with all continuous feed systems, the paper is not in a state of tension against the platen and is only loosely held.
In applying the plural steps of the divisional printing to paper in such a state, the paper unavoidably shifts in position. That is, the paper shifts in position in the course of the process of, for example, a first step, a second step, and a third step of the divisional printing.
Because of this shift in position of the paper, the plural patterns printed by divisional printing using a printing head sometimes are interspaced by gaps or partially overlap each other.
Such gaps or overlapping detracts from the quality of the print, and causes considerable problems in realizing satisfactory quality of the printed product.
An example of the prior art divisional printing system is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 58-71174.